1. Field of The Invention
The present invention relates to a circuit breaker for interrupting an electric circuit for a short time, and more particularly, to a circuit breaker integrally provided with a breaker portion for interrupting an electric circuit and a control portion for controlling the breaker portion.
2. Description of The Related Art
In an electrical component system provided in a vehicle, when something is wrong with a load of a power window or the like, or when something is wrong with a wire harness or the like constituted by a plurality of electric wires connecting a battery and various loads to each other, a high-current fuse inserted between the battery and the wire harness is blown out to interrupt a connection between the battery and the wire harness, thereby preventing the loads, the wire harness and the like from being burnt and damaged.
However, in the case of the electric component system using such a high-current fuse, even if something is wrong with the load of the power window or the like, or something is wrong with the wire harness or the like connecting the battery and various loads, the fuse is not blown out unless a current equal to or greater than a tolerated value which is previously set for the high-current fuse. Therefore, various protecting apparatuses have been developed for detecting the current and interrupt the connection between the battery and the wire harness when a high current close to the tolerated value is continuously flowing.
FIG. 1 is a sectional view showing one example of the protecting apparatus using a bimetal (Japanese Utility Model Application Laid-open No. S64-29756). The protecting apparatus shown in FIG. 1 is made of insulation resin, and comprises a housing 103 formed at its upper portion with a fuse accommodating portion 102, a lid 113 for closing the fuse accommodating portion 102 such that the latter can be opened and closed, a power source terminal 105 disposed in a lower portion in the housing 103 such that an upper end of the power source terminal 105 projects into the fuse accommodating portion 102 and a lower end thereof is exposed outside, and the exposed portion of the power source terminal 105 being connected to a positive terminal of a battery 104, a load terminal 109 disposed in a lower portion in the housing 103 such that an upper end of the load terminal 109 projects into the fuse accommodating portion 102 and a lower end thereof is exposed outside, and the exposed portion of the load terminal 109 being connected to a load 108 through an electric wire 107 constituting a wire harness 106, a fusible member 110 made of low-melting metal disposed in the fuse accommodating portion 102, and having one end connected to an upper end of the power source terminal 105 and the other end connected to an upper end of the load terminal 109, an intermediate terminal 111 disposed in a lower portion in the housing 103 such that the intermediate terminal 111 is located at an intermediate position between the power source terminal 105 and the load terminal 109 and a lower end of the intermediate terminal 111 is exposed outside, and the exposed portion being connected to a negative terminal of the battery 104, and a bimetal 112 which is made of a long plate-like member comprising two kinds of metal bonded together and which is disposed such as to be opposed to the fusible member 110 such that a lower end of the bimetal 112 is connected to an upper end of the intermediate terminal 111 and an upper end thereof being bent into an L-shape.
When an ignitor switch and the like of the vehicle are operated, and a current is flowing through a path comprising the positive terminal of the battery 104, the power source terminal 105, the fusible member 110, the load terminal 109, the electric wire 107 of the wire harness 106, the load 108, and the negative terminal of the battery 104, and when an abnormal condition occurs in the load 108 or in the wire harness 106 connecting the load 108 and a protecting apparatus 101, and a current equal to or greater than the tolerated value flows through the fusible member 110, the fusible member 110 is heated and blown out for protecting the load 108, the wire harness 106 and the like.
Further, even if something is wrong with the load 108 or the wire harness 106 connecting the load 108 and the protecting apparatus 101, and a large current flows through the fusible member 110, if the current does not exceed the tolerated value, the fusible member 110 is heated by the current following through the latter, and the bimetal 112 starts deforming. When a predetermined time is elapsed from the instant when the large current starts flowing through the fusible member 110, a tip end of the bimetal 112 comes into contact with the fusible member 110, and a large short-circuit current flows through the fusible member 110 in a path comprising the positive terminal of the battery 104, the power source terminal 105, the fusible member 110, the intermediate terminal 111, and the negative terminal of the battery 104, and the latter is blown out.
With the above structure, even when a current equal to or lower than the tolerated value flows for a preset time or longer, the circuit is interrupted to protect the wire harness 106 and the load 108.
As another protecting apparatus investigated by the present inventors rather than this protecting apparatus 101, a protecting apparatus 121 shown in FIG. 2 has been also developed (Japanese Utility Model Application Laid-open No. S64-29756).
The protecting apparatus 121 shown in FIG. 2 comprises a housing 122 made of insulation resin, a power source terminal 124 embedded in one side surface of the housing 122 and having a lower end connected to a positive terminal of a battery 123, and a load terminal 128 embedded in the other side surface of the housing 122 and having a lower end connected to a load 127 through an electric wire 126 constituting a wire harness 125. The protecting apparatus 121 further comprises an electric wire 131 including a fusible lead 129 which is made of low-melting metal and formed into U-shape and a heat-proof coating 130 formed such as to cover the fusible lead 129. The protecting apparatus 121 further comprises a coil 132. The coil 132 is made of shape-memory alloy which is formed into a shape wound around the electric wire 131 as shown in FIG. 2 when it is in a martensite phase state, and which is returned to its original phase shape fastening the electric wire 131 when it is heated from 120xc2x0 C. to 170xc2x0 C. The protecting apparatus 121 further comprises an external terminal 133 whose upper end is connected to one end of the coil 132 and whose lower end is connected to a negative terminal of the battery 123.
When an ignitor switch and the like of the vehicle are operated, and a current is flowing through a path comprising the positive terminal of the battery 123, the power source terminal 124, the fusible lead 129 of the electric wire 131, the load terminal 128, the electric wire 126 of the wire harness 125, the load 127 and the negative terminal of the battery 123, and when an abnormal condition occurs in the load 127 or in the wire harness 125 connecting the load 127 and a protecting apparatus 121, and a current equal to or greater than the tolerated value flows through the fusible lead 129, the fusible lead 129 is heated and blown out for protecting the load 127, the wire harness 125 and the like.
Further, even if something is wrong with the load 127 or the wire harness 125 connecting the load 127 and the protecting apparatus 121, and a large current flows through the fusible lead 129, if the current does not exceed the tolerated value, the fusible lead 129 is heated by the current flowing through the latter, and a temperature of the coil 132 rises. When a predetermined time is elapsed from the instant when the large current starts flowing through the fusible lead 129, and the temperature of the coil 132 rises to 120xc2x0 C. to 170xc2x0 C., the coil 132 changes from its martensite phase state to its original phase and bites into the heat-proof coating 130 which is softened by heat and comes into contact with the fusible lead 129, and a large short-circuit current flows through the fusible lead 129 in a path comprising the positive terminal of the battery 123, the power source terminal 124, the fusible lead 129, the coil 132, the external terminal 133, and the negative terminal of the battery 123, and the latter is blown out.
With the above structure, even when a current equal to or lower than the tolerated value flows for a preset time or longer, the circuit is interrupted to protect the wire harness 125 and the load 127.
However, in the above-described conventional protecting apparatuses 101 and 121, there are problems as follows.
First, in the case of the protecting apparatus shown in FIG. 1, it is detected whether a large current flows through the fusible member 110 using the bimetal 112 made of two kinds of metals having different thermal expansion coefficients and bonded to each other. Therefore, if the magnitude of the current is flowing through the fusible member 110, the bimetal 112 is deformed, and the time that elapsed before the circuit is interrupted is varied, depending on the current flowing therethrough.
Thus, when a failure that a large current flows intermittently occurs, a temperature of the fusible member 110 does not rise more than a certain value, and there is an adverse possibility that the wire harness 106 or the load 108 may be burnt before the protecting apparatus 101 interrupts the circuit.
In the case of the protecting apparatus 121 shown in FIG. 2, it is detected whether a large current flows through the fusible lead 129 using the coil 132 made of shape-memory alloy. Therefore, if the magnitude of the current is flowing through the fusible lead 129, the coil 132 is deformed, and the time that elapsed before the circuit is interrupted is variedxe2x80x94depending upon the flowing current.
Thus, when a failure that a large current flows intermittently occurs, a temperature of the fusible lead 129 does not rise more than a certain value, and there is an adverse possibility that the wire harness 125 or the load 127 may be heated excessively before the protecting apparatus 121 interrupts the circuit. Further, if the bimetal or shape-memory alloy is used, since the deformation-starting temperature is usually as low as about 100xc2x0 C., it is difficult to use it at 120xc2x0 C. to 125xc2x0 C. which is the using environment temperature condition of the vehicle.
Further, in the protecting apparatuses shown in FIGS. 1 and 2, the heat reaction time of the bimetal 112 or of the coil 132 which is a thermal-deformable electrical conduction member is varied depending upon the current flowing therethrough. Further, the heat reaction of the thermal-deformable electrical conduction member is not operated timely in some cases when an abnormal condition occurs (when excessive current flows).
It is an object of the present invention to provide a circuit breaker capable of reliably interrupting a circuit in a short time to protect an electrical part when an abnormal signal of a vehicle is inputed.
To achieve the above object, according to a first aspect of the present invention, there is provided a circuit breaker comprising a conductive heating portion disposed between a first connecting terminal and a second connecting terminal such that the heating portion is in contact with the first connecting terminal and the second connecting terminal and having a heating agent therein, an ignitor accommodated in the heating portion for igniting the heating agent charged in the heating portion when abnormal conditions of a vehicle are encountered, an expandable resilient member which is disposed such that the resilient member is in contact with the heating portion for pushing the heating portion, a melting member for maintaining the resilient member in its compressed state, a first container for accommodating the heating portion, the ignitor, the resilient member and the melting member, a detecting portion for detecting an abnormality of the vehicle, a judging portion for judging whether the vehicle is under abnormal conditions based on an output from the detecting portion and for outputting a driving control signal when the judging portion judged that the vehicle is under the abnormal conditions, a driving portion for operating the ignitor based on the driving control signal from the judging portion, and a second container for accommodating the detecting portion, the judging portion and the driving portion, and the second container being integrally assembled with the first container.
According to the first aspect, if the detecting portion detects an abnormality of the vehicle, the judging portion judges whether the vehicle is under the abnormal conditions based on the output from the detecting portion, and if the judging portion judged that the vehicle is under the abnormal conditions, the judging means output the driving control signal, and the driving portion operates the ignitor based on the driving control signal from the judging portion. Therefore, the ignitor ignites the heating agent charged in the heating portion, the melting member is melted by the heat of the heating agent, the compressed resilient member is expanded and the heating portion jumps up. Therefore, the electrical connection between the heating portion and the first and second connecting terminals is cut off, and the circuit can be interrupted.
Accordingly, since the second container accommodating the detecting portion, the judging portion and the driving portion, and the second container being integrally assembled with the first container accommodating the heating portion, the ignitor, the resilient member and the melting member, a non-operational state of the ignitor due to disconnection of electric wire is eliminated.
According to a second aspect of the invention, in the circuit breaker of the first aspect, the circuit breaker further comprises a connector having a terminator whose one end is electrically connected to the ignitor, and a substrate provided for mounting the detecting portion, the judging portion and the driving portion into the second container, and the other end of the terminal is soldered to the substrate, and the driving portion and the ignitor are electrically connected to each other through the substrate and the terminal.
According to the second aspect, the one end of the terminal of the connector is electrically connected to the ignitor, the other end of the terminal is soldered to the substrate on which the driving portion is mounted, and the driving portion and the ignitor are electrically connected to each other through the substrate and the terminal. Therefore, there is no connection using electric wire and thus, an adverse possibility that the ignitor 29 is erroneously operated due to noise is reduced.
According to a third aspect of the invention, in the circuit breaker of the second aspect, the connector is detachable with respect to the ignitor, and the connector is disengaged from the ignitor when the ignitor is moved by ignition of the heating agent.
According to the third aspect, when the ignitor is pushed upward and moved by ignition of the heating agent, the connector is disengaged from the ignitor, and the power supply to the ignitor can be automatically stopped. With this structure, the current does not keep flowing, heat is not transmitted to the substrate and the like and thus, the electronic such as the substrate and device is less prone to be damaged.
According to a fourth aspect of the invention, in the circuit breaker of the first aspect, the detecting portion is a current sensor for detecting a current flowing through at least one of the first connecting terminal and the second connecting terminal, and the judging portion judges whether a current value detected by the current sensor became equal to or greater than a preset threshold value, and if the current value detected by the current sensor became equal to or greater than the threshold value, the judging portion outputs the driving control signal to the driving portion.
According to a fifth aspect of the invention, in the circuit breaker of the first aspect, the melting member is made of resin member which is formed in the first container and which prevents a pushing force of the resilient member against the heating portion.
According to the fifth aspect, since the melting member formed in the first container is made of resin member which prevents a pushing force of the resilient member against the heating portion, the resin member can be melted and the heating portion and the ignitor can be lifted up when the heating agent is ignited.
According to a sixth aspect of the invention, in the circuit breaker of the first aspect, an end of the heating portion is formed with a side wall, and the side wall is connected to the first connecting terminal and the second connecting terminal through a low-melting material.
According to the sixth aspect, since the side wall is connected to the first connecting terminal and the second connecting terminal through the low-melting material, if the resin member and the low-melting material are melted by the heat of the heating agent, the heating portion jumps up, the electrical connection between the first and second connecting terminals is cut off and therefore, the circuit can reliably be interrupted within a short time to protect an electric part. Further, since the spring force is not applied to the low-melting metal which connects the first and second connecting terminals and the heating portion, it is possible to enhance the reliability of the connected portion.